Method of manufacturing semiconductor devices

Abstract

A method of manufacturing semiconductor devices is set forth using reactive ion plasma etching in which an optical grating is formed to etch underlying regions, such as dielectric material, semiconductor material, or alternate layers of different semiconductor material. The optical grating is formed with a rectangular profile having grooves and mask strips on a sample material where each of the grooves has a width L S substantially equal to the width L M of the mask strips. The optical grating is formed of a material which may be one of a photoresist, a dielectric compound, a metal, or a metallic compound. This method enables control of reactive ion etching during manufacture of integrated circuits of III-V compounds.

What is claimed is: 
     
       1. In a method of manufacturing semiconductor devices using reactive ion plasma etching which method comprises the steps of (a) forming an optical grating having a rectangular profile of grooves and mask strips on a sample material, each of said grooves having a width L s  and each of said mask strips having a width L m , where L s  is substantially equal to L m , said optical grating being formed of a material selected from one of a photoresist, a dielectric compound, a metal, or a metallic compound, and said sample material being formed of a material selected from one of a dielectric compound, a semiconductor compound, or alternate layers of different semiconductor material;   (b) illuminating said optical grating substantially perpendicularly to a surface of said optical grating with a laser beam, said laser beam having a wavelength λ, said widths L s  and L m  being larger in dimension than a dimension lc of the coherence zone of said laser beam;   (c) detecting specular reflection of said laser beam being reflected from said optical grating; and   (d) reactive ion etching said sample material through said optical grating.   
     
     
       2. A method according to claim 1, wherein said width L s  and said width L m  are each equal to 40 μm. 
     
     
       3. A method according to claim 1 or claim 2, wherein said wavelength λ of said laser beam is 632.8 nm. 
     
     
       4. A method according to claim 1 or claim 2, wherein said sample material is formed of a III-V group semiconductor compound. 
     
     
       5. A method according to claim 4, wherein said III-V group semiconductor compound is one of gallium arsenide (GaAs), gallium aluminum arsenide (GaAlAs), or indium phosphide (InP), and wherein said material of said optical grating is one of silica (SiO 2 ) or silicon nitride (Si 3  N 4 ). 
     
     
       6. A method according to claim 1 or claim 2, wherein when said step (d) of reactive ion etching is carried out, intensity of said reflected laser beam is measured as a first periodical curve of decreasing amplitude having a short period T 1  between two minima of said first periodical curve, and is measured as a second periodical curve of decreasing amplitude having a long period T 2  between two minima of a lower envelope of said first periodical curve, said second periodical curve being formed of said lower envelope and an upper envelope, wherein said first periodical curve is formed between said lower envelope and said upper envelope, and wherein said step (d) is begun at a time t o  and stopped at a time t 1 , said time t 1  being a function of data derived from said first and second periodical curves, wherein said data includes (A) an overall depth d G  etched into said sample material given by the relation   d.sub.G =N.sub.1 P.sub.1 +N.sub.2 P.sub.2 between t.sub.o and t.sub.1,        where N 1  is the number of short periods between t o  and t 1 , P 1  =λ/2n o , where n o  is the refractive index of air, N 2  is the number of long periods between t o  and t 1 , and P 2  =λ2n m  where n m  is the index of refraction of said material of said optical grating;   (B) a lateral dimension of l f  of etching edges of said sample material given by the relation   l.sub.f -l.sub.c =Kx difference of amplitudes        at time t between said lower envelope and said upper envelope, where K is a constant determined by modellization, where l f  =0 where the difference of the amplitudes is a maximum, and l f  =l c  when said difference of the amplitudes is zero; and   (C) a thickness d R  of roughness at the bottom of an etched groove given at said time t by the modellization of the decrease of minimum intensity of said lower envelope, said modellization resulting from simulation by a layer having an effective refractive index between that of air and that of said sample material.   
     
     
       7. A method according to claim 6, wherein measurement of said lateral dimension l f  at said etching edges at said time t is effected by measuring in a scanning electron microscope the lateral dimension l' f  of edges of a reference sample material under conditions l f  =l c  which is a constant of said optical grating. 
     
     
       8. A method according to claim 7, wherein said modellization for determining said thickness d R  is effected by measuring with spectroscopic ellipsometry a thickness of roughness d' R  of said reference sample material.